Semiconductor chips are tested individually or in wafer form. Contact surfaces, e.g., the bond pads, are electrically contacted on the chip and connected via a probe needle to a test circuit. Electronic test signals are applied to the circuit on the chip via this test circuit, and the response to these test signals is measured and evaluated. If behavior deviating from the desired function is determined, the measured chip is rejected as defective, or defect parameters for the subsequent correction of defects are determined.
In order to carry out the contact of the probe needle with the contact surfaces, the relative movement between the given probe needle and the corresponding contact surface and toward one another is necessary. This movement is generally designated as touchdown. The probe needle is provided with a tip in order to improve the contact of the probe needle with the contact surface.
However, in practice, the tips oxidize after a number of touchdowns and exhibit deformation. This results in greater contact resistance with the contact surfaces. But high mechanical stability of the contact tips and low contact resistance are of crucial importance in semiconductor measuring technology.
In present practice, various cleaning methods for the contact tips, such as intermediate contacting of adhesive films or cleaning of wafers, are used to increase measurement reliability. However, conventional cleaning methods result in increased curvature of the contact tips. Also, an increase of the so-called overdrive or a double touchdown is possible for breaking up the oxide on the needle tip. However, this results in damage to the contact pad, which has disadvantages in subsequent process steps, such as wire bonding, or in further contact for measuring purposes.
The contact tips are damaged when making contact with the contact surfaces of the semiconductor chips. On the one hand, this takes place by scratching the contact tips on the contact surface, which is partially intentionally produced in order to decrease the contact resistance. On the other hand, material is also torn from the surface of the contact tip as a result of microweldings that occur when a test voltage is applied. This damage to the contact tip results in unreliable measurements, high maintenance costs, and low service life of the probe needles. In particular, when probe cards are used, the low service life of the probe needles contributes to an early failure of the cost-intensive probe cards.
The use of probe needles for testing semiconductor structures has long been known in the prior art and is described, e.g., in U.S. Pat. No. 5,023,561 or in EP Patent No. 0 660 387 B1. These publications also concern the design of probe needles, particularly the shaping of the tips, but do not solve the basic problem.